1. Field of the Invention
The present invention relates generally to variable geometry turbochargers. More particularly, a turbocharger is provided having a sliding piston creating a variable nozzle turbine inlet with vanes extending across the nozzle in a closed position of the piston.
2. Description of the Related Art
High efficiency turbochargers employ variable geometry systems for turbine nozzle inlets to increase performance and aerodynamic efficiency. Variable geometry systems for turbochargers have typically been of two types; rotating vane and piston. The rotating vane type exemplified by U.S. Pat. No. 5,947,681 entitled PRESSURE BALANCED DUAL AXLE VARIABLE NOZZLE TURBOCHARGER provide a plurality of individual vanes placed in the turbine inlet nozzle which are rotatable to decrease or increase nozzle area and flow volume. The piston type, which is exemplified by U.S. Pat. Nos. 5,214,920 and 5,231,831 both entitled TURBOCHARGER APPARATUS, and U.S. Pat. No. 5,441,383 entitled VARIABLE EXHAUST DRIVEN TURBOCHARGERS, employs a cylindrical piston or wall which is movable concentric with the axis of rotation of the turbine to reduce the area of the nozzle inlet. In most cases, the piston type variable geometry turbocharger incorporates vanes with fixed angle of attack with respect to the airflow, which are either mounted to the piston or a stationary nozzle wall opposite the piston and are received in slots in the opposing surface during motion of the piston.
In piston type variable geometry turbochargers in the prior art, the challenge has been maximizing aerodynamic performance balanced with tolerancing of mating surfaces, particularly of vanes and receiving slots that are employed in most designs which are subjected to extreme temperature variation and mechanical stress, as well as providing means for actuating the piston in a readily manufacturable configuration.